KEVOS® MAKEOS · Power Transmission
Three-Phase Motor Power, Current and Torque
What current does this three-phase motor draw, or what power does a measured current mean?
Input power, output power, line current and shaft torque of a three-phase induction motor from voltage, power factor and efficiency.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Calculate | choice | Current from power, or power from a measured current. |
| Line voltage | V | Line-to-line supply voltage (e.g. 400 or 415 V). |
| Shaft output power | kW | Rated or required shaft power (current mode). |
| Measured line current | A | Measured line current (power mode). |
| Power factor | Power factor at this load from the motor data sheet (falls at part load). | |
| Efficiency | % | Efficiency at this load from the data sheet. |
| Shaft speed | rpm | Shaft speed (rated speed for full load). |
Method and formulas
- Input power P_in = √3 V I pf.
- Output power = P_in × efficiency; current I = P_out ÷ (√3 V pf η).
- Torque = 9549 × P_out (kW) ÷ n.
- Example: 11 kW at 415 V, pf 0.85 and 91% efficiency draws about 19.784 A.
Limitations
- Balanced three-phase supply; power factor and efficiency change with load.
- Not a substitute for the motor nameplate current or electrical code sizing rules.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate full-load current for cable and protection sizing
- Convert a measured current into load
- Find shaft torque from rated power and speed
Who it is for
- Electrical and maintenance engineers
- Design engineers
What you get
- Line current
- Electrical input power
- Shaft output power
- Shaft torque
Interpreting the result
- Size cables and protection from the nameplate current and your wiring rules (e.g. AS/NZS 3000 and 3008).
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2569–2580. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Three-Phase Motor Power, Current and Torque calculator
